The increase in the number of evacuations in frequency and quantity, characterized by a decrease in consistency and with a duration of less than 14 days.

Others alter the integrity of the mucosa through cytotoxic mediators, which may or may not invade the tissue.

Some have the ability to occupy tissue, which activates the host cell to initiate an energy-dependent process of endocytosis aided by the microfilament system of the intestinal mucosa (Shigella spp., enteroinvasive E. coli, rotavirus); this process leads to tissue invasion of the microorganism and destruction of the mucosa.

Some agents do not alter the mucosa, but lead to diarrhea secondary to the release of enterotoxins, which promote intestinal secretion (Sthaphylococcus aureus, Bacillus cereus, Clostridium botulinum).

The adhesion mechanism, which causes change in the structure of the villi, produces atrophy and interferes with the absorption of the luminal content (Giardia lamblia, rotavirus).

Evolves as bloody diarrhea and fever indicating damage to the colonic mucosa due to invasion of the colonic mucosa by pathogens or a toxin; it is usually in small amounts, associated with colicky abdominal pain, urgency, and tenesmus. Leukocytes in fecal mucus are positive. In immunocompromised patients, cytomegalovirus can cause intestinal ulceration with bloody diarrhea. In these cases, a differential diagnosis should be made with inflammatory bowel diseases.

It is of the watery type, not bloody, and is accompanied by colic, bloating, nausea, and vomiting, which suggest a small intestinal origin. It is generally caused by bacterial toxins from E. coli, Staphylococcus aureus, Bacillus cereus, Clostridium perfringens, and other agents that alter the intestinal mucosa and produce secretion. From a clinical point of view, it can be a moderate to voluminous diarrhea whose origin can be located in the small intestine. Usually, it can cause hydroelectrolyte imbalance. In these cases, leukocytes in fecal mucus are absent.

In the medical history it is important to highlight the following: place of residence such as asylum, pregnancy, recent trips, sexual practices, chronic-degenerative diseases, transplantation, recent hospitalization, consumption of medications, chemotherapy, radiation, state of malnutrition or immunosuppression.

Serum electrolytes and creatinine should be requested in cases with systemic toxicity and severe dehydration, especially in the elderly and patients with comorbidities. Complete blood count is indicated in diarrhea accompanied by fever and toxicity, leukocytosis and neutrophilia indicate an inflammatory bacterial pathogen and, in some cases, provide prognostic information.

The use of stool culture in the diagnosis of acute diarrhea is an ineffective and expensive tool

May be useful in the evaluation of persistent diarrhea and selected cases of acute diarrhea with colitis where the diagnosis is unclear, such as suspected toxin-negative Clostridium difficile; immunosuppressed patients due to the possibility of opportunistic agents that are difficult to diagnose, such as cytomegalovirus, especially with HIV infection.